Ridged waveguide fed scimitar antenna



Aug. 25, 1964 w. N. CARON RIDGED WAVEGUIDE FED SCIMITAR ANTENNA 2 Sheets-Sheet :2

Filed Jan. 31, 1962 ATTOR NEY United States Patent O 3,146,454 RIDGED WAVEGUIDE FED SCIMITAR ANTENNA Wilfred N. Caron, Arlington Heights, Ill., assignor to the United States of America as represented by the Secretary of the Air Force Filed Jan. 31, 1962, Ser. No. 170,290 10 Claims. (Cl. 343-848) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.

The purpose of this invention is to provide a method of exciting a waveguide, or of letting energy out of a waveguide through an open end. Heretofore, it has been customary to couple a waveguide to free space through the agency of a horn as an impedance matching device, or by means of an antenna to which the waveguide is coupled through a waveguide-to-coaxial transition. In accordance with the invention, a waveguide may be coupled to free space without the use of a horn or a waveguide-to-coaxial adapter. While it is not the intent of the invention to regulate the shape or size of the antenna, since these are determined by the nature of the application and the type of radiation pattern desired, the antenna most favored for this technique is a type of folded stub with diverging equiangular spiral boundaries known as the scimitar from its shape which resembles a scimitar blade. Antennas of this type are described, for example, in an article by Klass appearing on page 75 of Aviation Week for July 14, 1958. In any case, the matching is accomplished by the proper placement of the feed point of the antenna over the waveguide opening.

The invention will be described in more detail with reference to the specific embodinents thereof shown in the accompanying drawings in which- FIGS. la, lb, 2, 3, and 6 show couplings to scimitar type radiators, and

FIG. 4 shows a method of coupling to a broadband stub.

Referring to FIGS. la and lb, a rectangular waveguide 1 terminates in ground plane 2 provided by the surface of a circular metallic plate 3 which is designed to be mounted flush with the skin of an aircraft and held in place by screws for which holes 4 are provided. The longitudinal axis of the waveguide is normal to the ground plane. The antenna element 5 is of the scimitar type referred to above. The boundaries 6 and 7 of the antenna element are, from a point slightly beyond feed point 8, divergng spirals. This results in an increasing width of the antenna element as the distance from the feed point along the element increases. The element is both mechancally and electrically connected to the ground plane at the broad end 9.

In order to feed energy to the antenna at point 8, the waveguide as it approaches the ground plane undergoes a transition from a plain rectangular waveguide to a single ridge waveguide. This transition is accomplished by the tapered ridge which begins far enough back from the waveguide opening in the ground plane to provide a smooth transformation. Feed point 8 of the antenna is electrically connected to ridge 10 at the ground plane.

The placement of portion 11 of the antenna element 5, i.e., the portion just beyond feed point 8 that arches over the waveguide opening, is most important for proper performance of the antenna. Matching of the antenna to the waveguide is accomplished by moving this arch up or down or right or left, or by a combination of these movements, until a minimum VSWR is achieved. Minimun VSWR is achieved When the reactance of the antenna element 5 cancels the reactance of the waveguide opening.

A slightly difierent method of connecting the feed point of the antenna 5 to the waveguide is shown in FIG. 2. Here, as in FIGS. la and lb, the rectangular waveguide is transformed into a single ridge waveguide at the ground plane. In order to connect the feed point of the antenna to the waveguide the ridge, formed by element 10', is extended beyond the ground plane and the feed point 8 is connected thereto through a small cone 12 to give a more gradual transition from the waveguide to the antenna.

FIG. 3 shows an arrangement similar to the embodiment of FIGS. la and lb except for a slightly different Construction of the antenna element 5, which is characterized by a solid connection 13 between the feed point and base.

FIG. 4 illustrates the method of coupling a rectangular waveguide to a broadband stub antenna 14. Here, as in the embodiments of FIGS. la, lb, 2 and 3, the rectangular waveguide is transformed into a single ridge waveguide by means of the tapered ridge element 10'. The stub is connected to the ridge by means of a section 15 which arches over the end of the waveguide. The position of this section relative to the end of the waveguide is adjusted to give a minimum VSWR.

Two methods of coupling a double ridge waveguide 1' to a scimitar type antenna are shown in FIGS. 5 and 6. In FIG. 5, the double ridge waveguide is transformed into a single ridge waveguide by gradually increasing the height of ridge 16 and gradually decreasing the height of ridge 17 to zero. The coupling between ridge 16 and the antenna element 5 is the same as in FIG. 2. In the second method, shown in FIG. 6, the doubleridge waveguide is extended to -the ground plane, with ridge 16 being extended slightly beyond and coupled to the antenna in a manner similar to that shown in FIGS. 2 and 5.

I claim:

1. A waveguide fed antenna comprising: means providing a conductive ground plane surface; a waveguide of the ridge type opening into said ground plane surface and having a longtudinal aXis normal to said ground plane surface; and a folded stub antenna positioned on the opposite side of said ground plane surface with respect to said waveguide, said antenna having its feed point connected to a ridge of said waveguide and its other end in contact with said ground plane surface on the same side of said waveguide as said ridge.

2. A waveguide fed antenna comprising: means providing a conductive ground plane surface; a rectangular waveguide opening into said ground plane surface and having a longitudinal axis normal to said ground plane surface; means for transforming said rectangular waveguide into a single ridge waveguide at said ground plane surface; and a folded stub antenna positioned on the opposite side of said ground plane surface With respect to said waveguide, said antenna having its feed point connected to the ridge of said waveguide and its other end in contact with said ground plane surface on the same side of said waveguide as said single ridge.

3. A waveguide fed antenna comprising: means providing a conductive ground plane surface; a waveguide opening into said ground plane surface and having its longitudinal axis normal to said ground plane surface, said waveguide being initially of the dual ridge type and being gradually transformed into a single ridge type at said ground plane surface; and a folded stub an-tenna positioned on the opposite side of said ground plane surface with respect to said waveguide, said antenna having its feed point connected to the single ridge of said waveguide and having its other end in contact with said ground &1462454 plane surface on the same side of said waveguide as said single ridge.

4. A waveguide fed antenna comprising: means providing a conductive ground plane surface; a dual ridge waveguide opening into said ground plane surface, said waveguide having its longitudnal axis normal to said ground plane surface and having one ridge extended slightly beyond said surface; and a folded stub antenna positioned on the opposite side of said ground plane surface with respect to said Waveguide, said antenna having its feed point connected to the extended ridge of said waveguide and having its other end in contact with said ground plane surface on the same side of said Waveguide as said extended ridge.

5. A waveguide fed antenna comprising: means providing a conductive ground plane surface; a waveguide opening into said surface, said Waveguide having its longitudinal axis normal-to said surface and having a ridge extending slightly beyond said surface; and a folded stub antenna positioned on the opposite side of said surface with respect to said waveguide, said antenna having its feed point connected to the extended ridge of said waveguide and having its other end in contact with said surface on the same side of said wavegude as said extended ridge.

6. Apparatus as claimed in claim 1 in which said antenna comprises a metallic plate normal to said ground plane surface and to the longer dimension of said Waveguide and having boundaries that are spirals that diverge from the vicinity of the feed point to the end of the antenna in contact with said surface.

7. Apparatus as claimed in claim 2, in which said antenna comprises a metallic plate normal to said ground plane surface and to the longer dimension of said waveguide and having boundaries that are spirals that diverge from the vicinity of the feed point to the end of the antenna in contact with saidsurface.

8. Apparatus as claimed in claim 3, in which said antenna comprises a metallic plate normal to said ground plane surface and to the longer dimension of said waveguide and having boundaries that are spirals that diverge from the vicinity of the feed point to the end of the antenna in contact with said surface.

9. Apparatus as claimed in claim 4, in which said antenna comprises a metallic plate normal to said ground plane surface and to the longer dimension of said waveguide and having boundaries that are spirals that diverge from the vicinity of the feed point to the end of the antenna in contact with said surface.

10. Apparatus as claimed in claim S, in which said antenna comprises a metallic plate normal to said ground plane surface and to the longer dimension of said waveguide and having boundaries that are spirals that diverge from the vicinity of the feed point to the end of the antenna in contact with said surface.

References Cited in the file of this patent UNITED STATES PATENTS 2,658,145 Dorne et al. Nov. 3, 1953 2,933,705 Hopfer Apr. 19, 1960 2,943,275 Bittner et al. June 28, 1960 3,015,l01 Turner et al Dec. 26, 1961 

1. A WAVEGUIDE FED ANTENNA COMPRISING: MEANS PROVIDING A CONDUCTIVE GROUND PLANE SURFACE; A WAVEGUIDE OF THE RIDGE TYPE OPENING INTO SAID GROUND PLANE SURFACE AND HAVING A LONGITUDINAL AXIS NORMAL TO SAID GROUND PLANE SURFACE; AND A FOLDED STUB ANTENNA POSITIONED ON THE OPPOSITE SIDE OF SAID GROUND PLANE SURFACE WITH RESPECT TO SAID WAVEGUIDE, SAID ANTENNA HAVING ITS FEED POINT CONNECTED TO A RIDGE OF SAID WAVEGUIDE AND ITS OTHER END IN CONTACT WITH SAID GROUND PLANE SURFACE ON THE SAME SIDE OF SAID WAVEGUIDE AS SAID RIDGE. 